NOTES—WHAT IS DENSITY? Density is the amount of mass per unit of volume; it describes how much matter is packed into a space. Density is determined by its mass and volume

NOTES—WHAT IS DENSITY? Density is a characteristic property of matter A characteristic property does not depend on size (it will not change even if the amount of matter changes); therefore density is not dependent on the shape or amount of the substance 1mL of water has a density of 1g/mL 1000 mL of water has a density of 1 g/mL It is used to help identify one type of matter from another. The density of a pure substance is constant (at same temperature and pressure); it never changes.

CALCULATING DENSITY You need to measure an object’s mass and volume Density is calculated using the formula: Density = mass (g) ÷ Volume (mL or cm3) The basic unit for density is g/mL (liquid) or g/cm3 (solid or gas) D= m v

CALCULATING DENSITY When solving math problems, always show all work (even when using a calculator) STEPS: Write the formula Substitute measurements into formula Solve, label units and circle

Calculating density practice MUST SHOW WORK-DO ON LEFT SIDE OF NOTEBOOK Mass (g) Volume (cm3) Density (g/cm3 or g/mL) 200 200 mL 500 10 cm3 700 1000 mL

Why do substances either float or sink in a fluid? First, compare the density of the object/substance to the fluid it is in. If an object/substance is more dense than the fluid, it will sink If an object/substance is less dense than the fluid, it will float If an object/substance’s density is the same as the fluid, it won’t sink or float to the top; it will move toward the center of the fluid (neutral buoyancy)

How can you tell if something will float or sink in a fluid? The density of water is 1 g/mL. Do you know why ice floats on water? The density of ice is .92 g/cm3 For example: certain types of wood have a density of .8 g/cm3, so they will float in water. Steel has a density of 7.8 g/cm3, so it will sink in water. See it in action: http://www.teachersdomain.org/asset/phy03_vid_zoil/ http://www.pbs.org/wgbh/nova/balloon/science/density/fillingsans.html

Ships and boats are often made of steel. Why do they float on water? http://www.youtube.com/watch?v=zvRJ9FKTdC8 http://www.youtube.com/watch?v=xniW3_afO-0

How is density of matter effected by heat energy? As temperature increases, so does the amount of energy In general, the more energy a substance has: The more space between its molecules The less dense it is That’s why… Solids are usually the most dense phase of matter The molecules are tightly packed. Solids have little energy

How is density of matter effected by heat energy, continued? liquids are less dense than solids There is more space between the molecules liquids have more energy than solids An exception to the rule: Ice (H2O) is less dense than liquid water. Do you know why? Gases are the least dense state of matter There is lots of space between the molecules Gases have more energy than any phase

Does the density of a substance change if the amount changes? The density of a pure substance does not change if the size or amount changes For example: Find the density of a wooden block if mass=8g and volume= 10cm3 Density= ______ If the block is cut in half Mass= Volume= Density = Did the density change? No, because the ratio of mass to volume is all relative

STATES OF MATTER AND DENSITY

NOTES—WHAT IS DENSITY? Most dense least dense The more space between the atoms, the less dense the substance is. In general, solids are more dense than liquids liquids are much more dense than gases, but less dense than solids gases are the least dense of all